This relates to an electrosurgical instrument for performing laparoscopic surgical procedures, and more particularly to a laparoscopic electrosurgical instrument that is capable of grasping vessels and vascular tissue with sufficient force between two bipolar jaws to seal the vessel or vascular tissue.
Laparoscopic surgical instruments are used to perform surgical operation without making large incisions in the patient. The laparoscopic instruments are inserted into the patient through a cannula, or port, that has been made with a trocar. Typical sizes for cannulas range from three millimeters to twelve millimeters. Smaller cannulas are usually preferred, and this presents a design challenge to instrument manufacturers who must find ways to make surgical instruments that fit through the cannulas.
Certain surgical procedures require cutting blood vessels or vascular tissue. This sometimes presents a problem for surgeons because it is difficult to suture blood vessels using laparoscopic tools. Very small blood vessels, in the range below two millimeters in diameter, can often be closed using standard electrosurgical techniques. If a larger vessel is severed, it may be necessary for the surgeon to convert the laparoscopic procedure into an open-surgical procedure and thereby abandon the benefits of laparoscopy.
Several journal articles have disclosed methods for sealing small blood vessels using electrosurgery. An article entitled Studies on Coagulation and the Development of an Automatic Computerized Bipolar Coagulator, J. Neurosurg., Volume 75, Jul. 1991, describes a bipolar coagulator which is used to seal small blood vessels. The article states that it was not possible to safely coagulate arteries with a diameter larger than 2 to 2.5 mm. A second article is entitled Automatically Controlled Bipolar Electrocoagulationxe2x80x94xe2x80x9cCOA-COMPxe2x80x9d, Neurosurg. Rev. (1984), pp. 187-190. This article describes a method for terminating electrosurgical power to the vessel so that charring of the vessel walls can be avoided.
It has been recently determined that electrosurgical methods may be able to seal larger vessels using an appropriate electrosurgical power curve, coupled with an instrument capable of applying a large closure force to the vessel walls. It is thought that the process of coagulating small vessels is fundamentally different than electrosurgical vessel sealing. Coagulation is defined as a process of desiccating tissue wherein the tissue cells are ruptured and dried. Vessel sealing is defined as the process of liquefying the collagen in the tissue so that it crosslinks and reforms into a fused mass. Thus, coagulation of small vessels is sufficient to permanently close them. Larger vessels need to be sealed to assure permanent closure.
It would be desirable to have a surgical tool capable of applying electrosurgical energy, capable of applying a large closure force to the vessel walls, and also capable of fitting through a cannula. A large closure force between the jaws typically requires a large moment about the pivot for each jaw. This presents a challenge because the first and second pins have a small moment arm with respect to the pivot of each jaw. A large force, coupled with a small moment arm, is undesirable because the large forces may shear the first and second pins. It is also undesirable to increase the moment arm of the first and second pins because the physical size of the yoke might not fit through a cannula.
Several bipolar laparoscopic instruments are known. For example, U.S. Pat. No. 3,938,527 discloses a bipolar laparoscopic instrument for tubal cauterization. U.S. Pat. No. 5,250,047 discloses a bipolar laparoscopic instrument with a replaceable electrode tip assembly. U.S. Pat. No. 5,445,638 discloses a bipolar coagulation and cutting forceps with first and second conductors extending from the distal end. U.S. Pat. No. 5,391,166 discloses a bipolar endoscopic instrument having a detachable working end. U.S. Pat. No. 5,342,359 discloses a bipolar coagulation device.
The present invention solves the problem of providing a large closure force between the jaws of a laparoscopic bipolar electrosurgical instrument, using a compact design that fits through a cannula, without risking structural failure of the instrument yoke.
The present invention is an instrument for applying bipolar electrosurgical current to tissue in a laparoscopic operation with the added benefit of providing a large closure force between the instrument jaws. The large closure force may be particularly useful for vessel sealing operations. An advantage of the present invention is that tissue can be grasped and clamped with a relatively large closure force without damage to the yoke. The yoke is capable of transmitting the large closure force to the instrument jaws while being small enough to fit through a cannula The laparoscopic bipolar electrosurgical instrument comprises first and second jaws having, respectively, first and second flanges with first and second slots. The instrument is electrically connected to an electrosurgical generator, and conducts bipolar electrosurgical current to the first and second jaws. A yoke is attached to a pushrod and positioned to electrically insulate the first flange from the second flange. First and second pins on the yoke are designed to engage the first and second slots, respectively, in a cam-follower arrangement that opens and closes the jaws with linear motion of the yoke. The yoke is preferably a xe2x80x9cpush yokexe2x80x9d which means that linear motion of the yoke in the direction of the distal end of the instrument will cause the jaws to close together.
The yoke has first and second shoulders that are spaced apart from the first and second flanges until the jaws are in close arcuate proximity to each other. At that point, the first and second shoulders engage the first and second flanges, whereby further distal motion of the yoke applies a force to the first and second flanges that creates a moment about the pivot of each jaw. In general, the cam-follower arrangement of pins and slots may be designed to provide coarse motion of the jaws with relatively small forces. Large closure forces, once the jaws are relatively close together, may be obtained by pressing the shoulders against the flanges. The first and second pins move into cul-de-sacs in the first and second slots to protect them from large shear stresses when the shoulders are applying relatively large forces to the flanges. Thus, the first and second pins may be made from an electrically insulative material that is not designed to handle large shear stresses, large closure forces may be obtained, and the entire assembly may be compact and fit through a cannula
A method of making the laparoscopic bipolar electrosurgical instrument is described, comprising the following steps: forming a first jaw having a first flange with a first slot, and a second jaw having a second flange with a second slot; attaching a yoke to a pushrod; electrically insulating the first flange from the second flange with the yoke; engaging first and second pins with the first and second slots; positioning first and second cul-de-sacs respectively in the first and second slots to relieve shear stresses on the first and second pins at a subtended angle approximately wherein first and second shoulders engage the first and second flanges.